The Priority is a combination of the syslog facility and
severity. For example, LOG_ALERT | LOG_FTP sends an alert severity
message from the FTP facility. The default severity is LOG_EMERG;
the default facility is LOG_KERN.

const (
// From /usr/include/sys/syslog.h.
// These are the same up to LOG_FTP on Linux, BSD, and OS X.LOG_KERNPriority = iota << 3
LOG_USERLOG_MAILLOG_DAEMONLOG_AUTHLOG_SYSLOGLOG_LPRLOG_NEWSLOG_UUCPLOG_CRONLOG_AUTHPRIVLOG_FTPLOG_LOCAL0LOG_LOCAL1LOG_LOCAL2LOG_LOCAL3LOG_LOCAL4LOG_LOCAL5LOG_LOCAL6LOG_LOCAL7
)